Help with Toroidal Transformer

[bill south]

I have recently purchased off ebay a toroidal transformer with the following inputs/outputs: Two primaries constructed with about 14 gauge wire and three secondaries, 2 with approximately 10 gauge wire and 1 with 18 gauge wire. The price was right and I was going to re-wire the seconday for my 60 volt servos. However, I connected the first primary (white black) to 120 volts and my output was 39.7 volts on each of the high amp secondaries and 17 volts on the low amp secondary. I connected the other primary and got the same results on the secondaries (?). Also, I checked the voltage from one lead on one of the high amp secondaries to one of the leads on the other secondary and again got 39.7 volts, even though they are not physically connected (checked with an ohm meter). I figured this is some sort of induced voltage but that is just a guess while I'm trying to impress myself. Is this normal, the voltage, not impressing myself????
Now my questions, and forgive my ignorance! I'm trying to learn - safely!!!! Why would the transformer have two primaries??? Is there a way to load the secondaries with a resistor (or something) and determine what the maximum amperage is on the output or is there a formula or "rule of the thumb"??? Can I connect in parallel, both secondaries and get 2X the amperage, should I ever need it??? The transformer is physicall about 6" in Diameter and about 2" round and weighs a few ounces less than an ton. Is there a simple mount I can fabricate or where is a source I can purchase the mounts. I read somewhere that they should not be constructed of metal!
I kinda feel lucky in that the transormer was the correct voltage but I sure would like to know more about it and its maximum output so I don't go frying anything! (especially myself!).
As usual, all help is appreciated. This site is wonderful. I'm 53 years old and feel like a kid with a new toy during my lathemaster conversion. Thanks in advance!!!
billyjack

[Al_The_Man]

The two primaries are pretty certain to be used in parallel for 120 operation and in series for 240vac input, If you are reading the 'strange' voltage with a modern high impedance meter then the reading is due to capacitive coupling from one winding to the next, it would not support any kind of usefull current.
The mounting is typically a rubber cushion, top and bottom and a large metal disc that covers the top with a centre bolt through to the chassis, it does not matter if it is metal, as long as you do NOT have a metalic connection from the top disc around the OUTSIDE of the TXFR to chassis, you would then have a shorted turn.
10 Gauge wire is rated for 20amps so you can use that as a general guide line.
Al.

[ViperTX]

Well your primaries are 110 and 220 volt. Didn't the transformer have any spec.'s?

[bill south]

Gents;
Thanks for the information. No, the transformer did not have any specs. It was an ebay purchase and I bought it mainly as a learning tool and to rewind for my specific application. Turns out (no pun intended) that it is the correct voltage (just by luck). Should I wire the double 120 volt primaries and the double 39.7v secondaries in parallel or would that prove to be of any benefit??? I know I'll get double the amperage but my geckos are only good to 30 amps and the servos are rated at 11.9 amps stall current.
Thanks again. Shore am learning a lot!
billyjack

[Al_The_Man]

Yes, It would be benificial to parallel the windings, it doubles the current capacity, If they are not identified by the same colour for each sets then you should phase them before connecting, if you think you need to do that then that info. could be posted here.
Al.

[bill south]

Thanks Al;
I know I have seen posts on phaseing a transformer, but if it is not to inconvinient, I'd love a review of the procedure. I didn't know if phasing was applicable to a toroidal type of txfmr but it only makes sense that it would be. Thanks again.
billyjack

[Al_The_Man]

If intending to parallel.
On the primary connect both leads of one winding across the supply with ONE lead of the other windings connected to one of the these leads, then measure voltage from the open end of the second winding to the otherwise unconnected but powered lead of the first and there should be almost zero voltage, if you read a value equal to double the incomming supply then reverse the second winding connections.
The same with the secondary, except you just need to connect a lead from each winding to each other and leave the other two open, measure between the open two for zero volts.
Hope this is not as clear as mud
Al.